Knight Capital Group stopped taking new trading orders Wednesday afternoon as it struggled with "power issues" and requested its clients re-route all stock orders to other trading firms, according to two traders who received a memo from the firm.

Jersey City, N.J.,-based Knight plays a key role on Wall Street by acting as a middleman in the markets, completing investors' buy and sell orders.

The company's latest snafu comes as U.S. financial markets reopened after a two-day unexpected shutdown due to Superstorm Sandy. Though Wall Street is up and running, New York City continues to deal with the hurricane's aftermath, including widespread power outages and limited public transportation due to flooding.

Shares of Knight (KCG) fell as much as 8.4% Wednesday, before recovering to end the day little changed.

Earlier this year, Knight was rescued from bankruptcy after a trading glitch sent numerous erroneous orders in NYSE-listed securities into the market.